useleep_range() with a delta of 0 makes no sense and only prevents the timer subsystem from optimizing interrupts. As any user of usleep_range() is in non-atomic context the timer jitter is in the range of 10s of microseconds anyway. This adds a note making it clear that a range of 0 is a bad idea. Signed-off-by: Nicholas Mc Guire <hofrat@xxxxxxxxx> --- V2: trailing whitespaces removed (sent the wrong file before...) as of 4.9.0 there are about 20 cases of usleep_ranges() that have min==max and none of them really look like they are necessary, so it does seem like a relatively common misunderstanding worth noting in the documentation. Patch is against 4.9.0 (localversion-next is 20161212) Documentation/timers/timers-howto.txt | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/Documentation/timers/timers-howto.txt b/Documentation/timers/timers-howto.txt index 038f8c7..b5cdf82 100644 --- a/Documentation/timers/timers-howto.txt +++ b/Documentation/timers/timers-howto.txt @@ -93,6 +93,13 @@ NON-ATOMIC CONTEXT: tolerances here are very situation specific, thus it is left to the caller to determine a reasonable range. + A range of 0, that is usleep_range(100,100) or the + like, do not make sense as this code is in a + non-atomic section and a system can not be expected + to have jitter 0. For any non-RT code any delta + less than 50 microseconds probably is only preventing + timer subsystem optimization but providing no benefit. + SLEEPING FOR LARGER MSECS ( 10ms+ ) * Use msleep or possibly msleep_interruptible -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
